Regulation of Skeletal Muscle Mechanics: Chronic Influences On Acute Control

Abstract

Austin RicciDoctor of Philosophy in Human Physiology Title: Regulation of Skeletal Muscle Mechanics: Chronic Influences on Acute Control Skeletal muscle mechanics are dynamically regulated by chronic stressors such as resistance training (RT), age, and circulating sex hormones as well as acute stressors such as muscle activation and fatigue. Regulatory proteins within the sarcomere influence the interactions between myosin and actin and therefore alter muscle function at the most basic level. How these proteins are modified by the interplay between chronic and acute stressors may help explain why certain at-risk populations are unable to maintain muscle function during repeated muscle contractions or exercise. We hypothesized that fatiguing exercise to task failure induces post-translational modifications to key regulatory proteins, MyBP-C and RLC, that are associated with altered contractile function of individual muscle fibers in young recreationally active, young RT, and older adults. It has also been shown that estrogen deficiency leads to reduced RLC phosphorylation and the ability to potentiate force following brief muscle activation, but this has not been studied in humans. A separate study utilized a novel model of estrogen suppression in young females to study the effects of estrogen deficiency independent of age on RLC phosphorylation and whole muscle twitch potentiation in humans. Overall, we found that fatigue paradoxically improved contractile velocity and power in single muscle fibers of young adults, more prominently in RT young adults, but not in older adults. We also found that estrogen suppression in young females may lead to reduced twitch potentiation in vivo. These set of studies shed light on how chronic effectors influence acute control of muscle contractile function at the cellular and whole tissue level.